During blood flow, fluid mechanical forces cause increased numbers of platelets at the wall compared with the number that would be predicted from platelet counts of bulk, static blood. The flow dependence of the increased number is uninvestigated; previous work indicates that the wall concentration may have a maximum value at an intermediate value of the wall shear rate. The proposed work uses the generalized Fahraeus effect, which occurs in capillary tubes, to experimentally investigate the flow dependence of the wall concentration of platelets. Specific methods are described by which experimental blood samples can be accurately collected and evaluated on a Coulter counter. Individual variables that will be investigated include wall shear rate, tube diameter, entry length, hematocrit, platelet count and anticoagulant. Experiment results of the tube platelet count will be interpreted via two models of platelet wall concentration. The first model is one-dimensional, integral form of mass-conservation for multi-phase flow. The proposal reviews assumptions which make this simple model determinate. In the second, more complex model of mass conservation in a flowing system, the platelet concentration in the marginal layer is controlled by three competing fluxes, which are driven by the repulsive, shear-induced wall force and gradients of diffusivity and concentration. Diffusion in the marginal layer is treated as a combination of Brownian and shear-enhanced diffusion. The results of the proposed work will further the understanding of the general relationship among flow, thrombosis, and sub-lethal platelet damage by showing how flow changes the number of platelets that are exposed to the wall. The results will aid rational design of tests for blood-compatible biomaterials and artificial internal organs.